In general, an electrospinning apparatus for producing nanofibers includes: a spinning solution (polymer solution) storage tank; a spinning solution quantitative transfer device; a nozzle block; a plurality of nozzles provided to the nozzle block; a collector for collecting nanofibers spun through the nozzles; and a power supply for applying voltage across the nozzle block and the collector.
When nanofibers are produced using such a typical electrospinning apparatus, the types of used polymer and solvent, the concentration of a polymer solution, and the temperature and humidity of a spinning room may affect the diameter of spun nanofibers and spinning efficiency. Hereinafter, the term “humidity” denotes “relative humidity”.
In general, as the molecular weight of a polymer increases, the viscosity of a polymer solution increases so as to increase the diameter of spun nanofibers. Since the boiling point (volatilization temperature) of a solvent of a polymer solution affects a solidification speed of the polymer solution, the boiling point (volatilization temperature) of a solvent directly affects the diameter of nanofibers in a region (that is, a spinning zone) where nanofibers are produced from a polymer solution through a jet stream. That is, when the boiling point of a solvent is low, the solidification speed of the solvent is increased to increase the diameter of nanofibers. On the contrary, when the boiling point of a solvent is high, the diameter of nanofibers is decreased.
As the concentration of a solution increases, the surface tension and activation energy of the solution increase so as to increase the diameter of produced nanofibers. On the contrary, as the concentration of a solution decreases, the diameter of produced nanofibers is decreased.
The temperature of a region where an electrospinning process is performed (hereinafter, referred to as a “spinning zone”) varies the viscosity of a spinning solution so as to change the surface tension of the spinning solution, thereby affecting the diameter of produced nanofibers.
That is, when the temperature of a spinning zone is increased to decrease the viscosity of a solution, the diameter of produced nanofibers is decreased. On the contrary, when the temperature of a spinning zone is decreased to increase the viscosity of a solution, the diameter of produced nanofibers is increased.
When the humidity of a spinning zone is increased in order to decrease the diameter of nanofibers, the volatilization speed of a solvent is decreased, which may cause a film defect that jeopardizes the cleanliness of a product. To address such a film defect, a discharge rate of a solution should be decreased, which sacrifices productivity. On the contrary, when the humidity of a spinning zone is decreased to increase productivity, the volatilization speed of a solvent is increased to increase the solidification speed of nanofibers, thus increasing the diameter thereof. As described above, in order to produce nanofibers having stable quality through an electrospinning process, it is important to uniformly maintain the temperature and humidity of a space where an electrospinning process is performed, that is, the temperature and humidity of a spinning zone.
Korean Patent No. 10-549140 discloses an electro-blowing spinning technology in which an air injection port is disposed around a spinning nozzle for spinning a polymer solution, to inject compressed air at high speed to nanofibers spun from the spinning nozzle.
In this case, although a typical electro-blowing spinning apparatus is appropriate to massively produce nanofibers, since injected air is within in a turbulence flow region and a transition range, an air turbulence may occur in a spinning zone to thereby destabilize the solidification speed of nanofibers. As a result, the diameter and diameter variation of produced nanofibers are increased as illustrated in FIGS. 7 and 8.
When nanofibers having uniform diameters are produced using a typical electrospinning apparatus, the entire temperature and humidity of a spinning room should be uniformly maintained according to predetermined conditions. To this end, an air conditioner system is installed on the spinning room. However, such air conditioner systems increase equipment and energy costs.